Touch panel device and contact position detection method

ABSTRACT

A burst wave is applied to an excitation element of a touch panel main body from an oscillation section so as to excite surface acoustic waves, and the excited surface acoustic waves are received by a receiving element of the touch panel main body. The received signals are A/D converted by a receiving section, and a control section calculates the contact position and the contact width of the object in contact with the touch panel main body, based on time-series changes in the received strength. Based on the received strength of surface acoustic waves, the control section controls the wave number of the burst wave to be applied to the excitation element.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of Ser. No. 10/696,037,filed Oct. 30, 2003, which is based upon and claims the benefit ofpriority from the prior Japanese Patent Application No. 2002-320423,filed Nov. 1, 2002, the entire contents of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

The present invention relates to a touch panel device for detecting thecontact of an object, such as a finger or a pen, with the touch paneldevice, and more particularly relates to a touch panel device and acontact position detection method, for detecting the contact position ofthe object by detecting attenuation and cutoff of surface acoustic waves(SAWs).

With the spread of computer systems, mainly personal computers, therehas been used a device for inputting new information or giving variousinstructions to a computer system by pointing at a position on thedisplay screen of a display device on which information is displayed bythe computer system, with a finger or a pen. In order to perform aninput operation with respect to the information displayed on the displayscreen of the display device of a personal computer or the like by atouching method, it is necessary to detect the contact position (pointedposition) on the display screen with high accuracy.

Well known examples of a touch panel device for detecting the contactposition of an object such as a finger or a pen are a device using aresistance film, and a device using ultrasonic waves. The former deviceusing a resistance film detects a change in the resistance of theresistance film caused by contact of the object with the resistancefilm. This device has the advantage of low consumption of power, but hasproblems in the aspects of the response time, detection performance anddurability.

By contrast, in the device using ultrasonic waves, the contact positionof an object such as a finger or a pen is detected by propagatingsurface acoustic waves on a non-piezoelectric substrate, for example,and detecting attenuation of the surface acoustic waves caused bycontact of the object with the non-piezoelectric substrate. In general,this touch panel device has a structure in which a burst wave is appliedto cause a transducer to generate surface acoustic waves, the generatedsurface acoustic waves are propagated on the non-piezoelectricsubstrate, the propagated surface acoustic waves are received, and thecontact position of the object is obtained based on the receivedresults. A variety of such touch panel devices have been proposed (forexample, Japanese Patent Application Laid-Open No. 7-319613/1995).

The present inventor et al. is conducting research and development on atouch panel device that uses, as a transducer, an IDT (inter digitaltransducer: comb-like electrode) that can be produced collectively usinga photolithography technique. In this touch panel device, an elementcomposed of an IDT and a piezoelectric thin film is used as each ofexcitation elements for exciting surface acoustic waves and receivingelements for receiving propagated surface acoustic waves.

FIG. 1 is an illustration showing the configuration of such a touchpanel device using IDTs. In FIG. 1, the numeral 61 represents arectangular non-piezoelectric substrate. A plurality of excitationelements 62, each composed of an input IDT and a piezoelectric thinfilm, for exciting surface acoustic waves are arranged in a line on oneend of each of the X-direction and the Y-direction of thenon-piezoelectric substrate 61 so that the excitation elements 62correspond to a plurality of tracks, respectively. Moreover, a pluralityof receiving elements 63, each composed of an output IDT and apiezoelectric thin film, for receiving surface acoustic waves arearranged in a line on the other end of each of the X-direction and theY-direction of the non-piezoelectric substrate 61 so that the receivingelements 63 face the excitation elements 62.

In this touch panel device, a burst wave is applied to each of theexcitation elements 62 to excite surface acoustic waves and propagatethem on the non-piezoelectric substrate 61, and then the propagatedsurface acoustic waves are received by the receiving elements 63. Whenan object such as a finger or a pen is in contact with the propagationpath of a surface acoustic wave on the non-piezoelectric substrate 61,the surface acoustic wave attenuates. Accordingly, by detecting whetheror not the level of the received signals at the receiving elements 63 isattenuated, it is possible to detect the presence or absence of contactof the object and the contact position.

In addition, the present inventor et al. proposed a touch panel devicein which the excitation elements and the receiving elements are arrangedso as to propagate surface acoustic waves in oblique directions(diagonal directions) of the substrate. FIG. 2 is an illustrationshowing an example of the electrode structure of such a touch paneldevice. In FIG. 2, the numeral 70 represents a rectangularnon-piezoelectric substrate made of glass material, and a center portionenclosed by the broken line is a detection region 70 a capable ofdetecting the contact position.

In a frame region outside the detection region 70 a, which is aperipheral section of the non-piezoelectric substrate 70, four IDTs 71are disposed. Each IDT 71 comprises facing bus electrodes 72, andcomb-like electrode fingers 73 which are extended from the buselectrodes 72 by turns and bent in the middle. In this structure, linesof comb-like electrode fingers 73 tilted in two directions from thefacing direction of the bus electrodes 72 are formed, thereby realizingexcitation of surface acoustic waves in two directions and reception ofsurface acoustic waves from two directions. In this example, the IDTs 71on the upper side and the lower side function as excitation elements forsimultaneously exciting surface acoustic waves in two differentdirections, while the IDTs 71 on the left side and the right sidefunction as receiving elements for simultaneously receiving surfaceacoustic waves from two different directions.

In the touch panel device having the structure shown in FIG. 1 or FIG.2, two pairs or four pairs of electrode groups are used, and the contactposition and/or the contact width of the object are calculated fromtime-series changes in the received strength of surface acoustic waves(the time domain waveform). The S/N of the received signal isproportional to the number of pairs of electrodes included in theaperture of the receiving element that receives the surface acousticwave. Therefore, since the number of times of driving of the surfaceacoustic wave (the wave number of the burst wave applied) for maximizingthe strength of surface acoustic waves to be received is determined bythe electrode structure, a fixed number of burst wave, which isdetermined by a design value or determined at the time of activation, isapplied to the excitation elements. Besides, a fixed threshold valuedetermined at the time of design or activation is used when calculatingthe contact position and the contact width.

However, since there is a difference in the performance between therespective electrode pairs, even when the burst wave of the same wavenumber is applied to propagate the surface acoustic waves, there is avariation in the received strength of the time domain waveform. Thus,when calculating the contact position and the contact width using thefixed threshold value determined at the time of design or activation,differences occur in touch sensitivity on the panel. Moreover, when thepanel is dirty with finger prints, etc., the received strength of thetime domain waveform varies. As a result, when the panel gets moredirty, the touch sensitivity gradually decreases, and there arises theproblem that high pressure of object (tool force when a pen is used) isnecessary to calculate the contact position and the contact width.Further, although at least two channels of receiving signals arenecessary to calculate the contact position and the contact width, thereis the case where the necessary pressure of the object for calculationdiffers between the respective channels, and only one channel is valid.In such a case, there is the problem that the contact position andcontact width of the object cannot be correctly calculated. Therefore,the present inventor el al. continues to conduct further research anddevelopment to solve these problems.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a touch panel deviceand a contact position detection method capable of always achievingstable touch sensitivity, even when there is a change in strength of thetime domain waveform because of finger prints, etc., by controlling thewave number of a burst wave, according to the received strength ofsurface acoustic waves.

Another object of the present invention is to provide a touch paneldevice and a contact position detection method, capable of accuratelydetecting the contact position of an object, without requiring highpressure of the object even when the panel is dirty, by controlling thewave number of a burst wave, according to the received strength ofsurface acoustic waves.

Still another object of the present invention is to provide a touchpanel device capable of eliminating the influence of noise and improvingthe detection accuracy of the contact position by smoothing the obtainedtime domain waveform.

Yet another object of the present invention is to provide a touch paneldevice capable of detecting the contact position without beinginfluenced by a constant change in the time domain waveform caused bydirt or the like on the panel by updating the waveform as a comparisonbase which is stored for use in calculating the contact position.

A further object of the present invention is to provide a touch paneldevice capable of correcting the deviation of the contact position dueto the wave number of the burst wave and improving the detectionaccuracy by detecting the contact position and/or the contact width ofan object, based on the attenuation start position and attenuation endposition and the wave number of the burst wave, or based on theattenuation start position and maximum attenuation position and the wavenumber of the burst wave.

A further object of the present invention is to provide a touch paneldevice capable of identifying a correct contact position by selecting acontact position with a larger contact width when a plurality of contactpositions are detected.

A further object of the present invention is to provide a touch paneldevice capable of achieving uniform detection sensitivity on the panelby correcting the strength of the time domain waveform, according to thepropagation distance.

A further object of the present invention is to provide a touch paneldevice capable of eliminating an erroneously detected contact positionby measuring the distance between contact positions detected every fixedtime interval and invalidating the contact position when the distance islonger than a predetermined value.

A touch panel device according to a first aspect of the presentinvention is a touch panel device having at least one pair of excitingmeans for exciting surface acoustic waves by application of a burst waveand receiving means for receiving surface acoustic waves, which arearranged to face each other on a substrate capable of propagatingsurface acoustic waves, for propagating surface acoustic waves betweenthe exciting means and the receiving means on the substrate anddetecting a position of an object in contact with the substrate, basedon received results by the receiving means, and comprises: measuringmeans for measuring strength of surface acoustic waves received by thereceiving means; and control means for controlling the wave number ofthe burst wave to be applied to the exciting means, based on thestrength of surface acoustic waves measured by the measuring means.

In the first aspect, the strength of surface acoustic waves received bythe receiving means is measured, and the wave number of the burst waveto be applied to the exciting means is controlled based on the measuredstrength of surface acoustic waves. Specifically, when the strength ofthe received surface acoustic waves is lower than a predetermined value,the wave number of the burst wave is increased. Accordingly, even whenthe strength of surface acoustic waves to be received changes due tofinger prints, etc., high touch sensitivity can be always obtained in astable manner. As a result, even when the touch panel is dirty, thecontact position of the object can be highly accurately detected withoutapplying high pressure of the object (tool force).

According to a touch panel device of a second aspect of the presentinvention, in the first aspect, the measuring means measures thestrength of surface acoustic waves with the passage of time, and thecontrol means controls the wave number of the burst wave, based on achange in strength of the surface acoustic waves with the passage oftime which is measured over a predetermined period by the measuringmeans.

In the second aspect, the strength of the received surface acousticwaves is measured with the passage of time, and the wave number of theburst wave is controlled based on a change in strength of the surfaceacoustic waves with the passage of time which is measured over apredetermined period. Accordingly, it is possible to achieve uniformtouch sensitivity when the strength of the time domain waveform changes.

A touch panel device according to a third aspect of the presentinvention is a touch panel device having at least one pair of excitingmeans for exciting surface acoustic waves and receiving means forreceiving surface acoustic waves, which are arranged to face each otheron a substrate capable of propagating surface acoustic waves, forpropagating surface acoustic waves between the exciting means and thereceiving means on the substrate and detecting a position of an objectin contact with the substrate, based on received signals by thereceiving means, and comprises smoothing means for smoothing thereceived signals of surface acoustic waves received by the receivingmeans.

In the third aspect, in order to eliminate noise included in thereceived signals of surface acoustic waves received by the receivingmeans, a smoothing process is performed on the received signals by amoving-average method or other method. Consequently, the influence ofnoise is eliminated, and the detection accuracy of the contact positionis improved.

A touch panel device according to a fourth aspect of the presentinvention is a touch panel device having at least one pair of excitingmeans for exciting surface acoustic waves by application of a burst waveand receiving means for receiving surface acoustic waves, which arearranged to face each other on a substrate capable of propagatingsurface acoustic waves, for propagating surface acoustic waves betweenthe exciting means and the receiving means on the substrate anddetecting presence or absence of an object in contact with thesubstrate, based on received results by the receiving means, andcomprises: storing means for storing received results by the receivingmeans about surface acoustic waves propagated when no object is incontact with the substrate; and comparing means for comparing receivedresults by the receiving means about surface acoustic waves propagatedwhen an object is in contact with the substrate with the receivedresults stored in the storing means.

In the fourth aspect, the received results of surface acoustic waveswhen no object is in contact with the substrate are stored, and thestored received results and received results of surface acoustic waveswhen an object is in contact with the substrate are compared, and thecontact position is detected based on the comparison result. Thus, sincea fixed threshold value which is determined during design or activationis not used as in a conventional art, even when the panel is dirty andhas a low touch sensitivity, it is possible to correctly detect thecontact position of the object.

According to a touch panel device of a fifth aspect of the presentinvention, in the fourth aspect, the touch panel device furthercomprises updating means for updating the received results stored in thestoring means.

In the fifth aspect, the received results of surface acoustic waveswhich are received when no object is in contact with the substrate andare stored are periodically updated. Therefore, since the dirt on thepenal is reflected in the received results as the comparison base, it ispossible to correctly detect the contact position of the object withoutbeing influenced by constant change in the time domain waveform causedby the dirt on the panel.

According to a touch panel device of a sixth aspect of the presentinvention, in the fourth or fifth aspect, the touch panel devicecomprises: calculating means for calculating an attenuation startposition and an attenuation end position of received surface acousticwaves, based on the comparison result obtained by the comparing means;and detecting means for detecting a contact position and/or a contactwidth of the object, based on the attenuation start position andattenuation end position calculated by the calculating means and thewave number of the burst wave applied to the exciting means.

In the sixth aspect, the attenuation start position and the attenuationend position of received surface acoustic waves are calculated, and thecontact position and/or the contact width of the object are detectedbased on these attenuation start position and attenuation end positionand the wave number of the burst wave applied to the exciting means.Accordingly, it is possible to correct the deviation of the contactposition due to the wave number of the burst wave, and improve thedetection accuracy of the contact position and/or the contact width.

According to a touch panel device of a seventh aspect of the presentinvention, in the fourth or fifth aspect, the touch panel devicecomprises: calculating means for calculating an attenuation startposition and a maximum attenuation position of received surface acousticwaves, based on the comparison result obtained by the comparing means;and detecting means for detecting a contact position and/or a contactwidth of the object, based on the attenuation start position and maximumattenuation position calculated by the calculating means and the wavenumber of the burst wave applied to the exciting means.

In the seventh aspect, the attenuation start position and maximumattenuation position of received surface acoustic waves are calculated,and the contact position and/or the contact width of the object aredetected based on these attenuation start position and maximumattenuation position and the wave number of the burst wave applied tothe exciting means. Accordingly, it is possible to correct the deviationof the contact position due to the wave number of the burst wave, andimprove the detection accuracy of the contact position and/or thecontact width.

A touch panel device according to an eighth aspect of the presentinvention is a touch panel device having at least one pair of excitingmeans for exciting surface acoustic waves and receiving means forreceiving surface acoustic waves, which are arranged to face each otheron a substrate capable of propagating surface acoustic waves, forpropagating surface acoustic waves between the exciting means and thereceiving means on the substrate and detecting a position of an objectin contact with the substrate, based on received results by thereceiving means, and comprises: means for judging whether or not aplurality of contact positions are detected; calculating means forcalculating a contact width of the object for each of the plurality ofcontact positions when the plurality of contact positions are detected;means for comparing a plurality of the calculated contact widths; andmeans for determining that the contact position with the largest contactwidth is the contact position of the object.

In the eighth aspect, when a plurality of contact positions aredetected, since only one correct contact position is present, thecontact width of the object is calculated for each of these plurality ofcontact positions, and the contact position with the largest contactwidth is determined to be the contact position of the object. It is thuspossible to easily identify the correct contact position.

A touch panel device according to a ninth aspect of the presentinvention is a touch panel device having at least one pair of excitingmeans for exciting surface acoustic waves and receiving means forreceiving surface acoustic waves, which are arranged to face each otheron a substrate capable of propagating surface acoustic waves, forpropagating surface acoustic waves between the exciting means and thereceiving means on the substrate and detecting a position of an objectin contact with the substrate, based on received results by thereceiving means, and comprises correcting means for correcting strengthof surface acoustic waves received by the receiving means, according topropagation distances of surface acoustic waves.

In the ninth aspect, the strength of received surface acoustic waves iscorrected according to the propagation distances of surface acousticwaves. Since a surface acoustic wave that propagates in a long distancehas larger attenuation compared to a surface acoustic wave thatpropagates in a short distance, the received strength of surfaceacoustic waves is corrected to compensate for the difference in theattenuation. Consequently, it is possible to achieve uniform touchsensitivity of the panel irrespective of the propagation distances.

A touch panel device according to a tenth aspect of the presentinvention is a touch panel device having at least one pair of excitingmeans for exciting surface acoustic waves and receiving means forreceiving surface acoustic waves, which are arranged to face each otheron a substrate capable of propagating surface acoustic waves, forpropagating surface acoustic waves between the exciting means and thereceiving means on the substrate and detecting a position of an objectin contact with the substrate, based on received results by thereceiving means, and comprises: memory means for storing contactpositions of the object detected at predetermined time intervals; meansfor calculating a distance between a contact position detected justbefore and a contact position detected subsequently; and means forjudging whether or not the calculated distance is larger than apredetermined value, wherein, if the calculated distance is larger thanthe predetermined value, the subsequently detected contact position isinvalidated.

In the tenth aspect, in a plurality of contact positions detected in atime series, the distance between adjacent contact positions in time iscalculated, and, if the calculated distance is longer than apredetermined value, the succeeding contact position is invalidated.Accordingly, it is possible to easily eliminate an erroneously detectedcontact position.

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an illustration showing the configuration of a conventionaltouch panel device;

FIG. 2 is an illustration showing an example of the electrode structureof a conventional touch panel device;

FIG. 3 is an illustration showing the basic configuration of a touchpanel device according to the present invention;

FIG. 4 is an illustration showing the configuration of a touch panelmain body;

FIG. 5 is a flow chart showing the operating procedure of the touchpanel device of the present invention;

FIG. 6 is an illustration showing one example of a time domain waveform;

FIG. 7 is an illustration showing a difference in the time domainwaveform when the wave number of a burst wave is varied;

FIG. 8 is an illustration showing a time domain waveform includingnoise;

FIG. 9 is an illustration showing the time domain waveforms (referencetime domain waveform and slice time domain waveform) as the comparisonbase;

FIG. 10 is an illustration showing the principle of obtaining theattenuation start position and the attenuation end position;

FIG. 11 is an illustration showing the principle of calculating thecontact position and the contact width;

FIG. 12 is an illustration showing the principle of obtaining theattenuation start position and the maximum attenuation position;

FIG. 13 is an illustration showing the principle of calculating thecontact position and the contact width;

FIG. 14 is an illustration showing the time domain waveforms when dirtis adhering to the panel;

FIG. 15 is an illustration showing the reference time domain waveformand slice time domain waveform after update;

FIG. 16 is an illustration showing the relationship between the actualtime domain waveform and the slice time domain waveform when contactpositions are detected at two points;

FIG. 17 is a flowchart showing the operating procedure for determiningone contact position from a plurality of contact positions, based on thecontact width;

FIG. 18 is an illustration explaining the principle of the receivingsignal correction process (smoothing process); and

FIG. 19 is an illustration showing the principle of eliminating anabnormal contact position among a plurality of contact positions.

DETAILED DESCRIPTION OF THE INVENTION

The following description will explain the present invention in detailwith reference to the drawings illustrating an embodiment thereof.

FIG. 3 is an illustration showing the basic configuration of a touchpanel device according to the present invention. The touch panel deviceof the present invention comprises: a touch panel main body 1 includingexcitation elements for exciting surface acoustic waves, a substrate forpropagating surface acoustic waves, and receiving elements for receivingsurface acoustic waves; and a touch panel drive device 2 for controllingthe excitation/receiving of surface acoustic waves in the touch panelmain body 1 and for calculating the contact position and contact widthof an object in contact with the touch panel main body 1.

The touch panel drive device 2 is functionally divided into threesections, namely, an oscillation section 3 for controlling theexcitation of surface acoustic waves, a receiving section 4 forcontrolling the receiving of surface acoustic waves, and a controlsection 5 for controlling the calculation of the contact position andcontact width of the object and the operations of the oscillationsection 3 and the receiving section 4. The oscillation section 3 and thecontrol section 5 are connected through a bus, and the receiving section4 and the control section 5 are connected through a bus.

The oscillation section 3 has a frequency controller (PLL) 31, anoscillator (VCO) 32, and a frequency counter 33. In the frequencycounter 33, a frequency specified by the control section 5 is set. Thefrequency controller 31 controls the driving frequency of the oscillator32, according to the set content. Note that the number of times ofcontinuous occurrence of driving frequency (the wave number of a burstwave) is specified by the control section 5. The receiving section 4 hasan amplifier 41 with the peak hold function for amplifying receivedsignals, and an A/D converter 42 for sampling time-series receivedsignals and outputting them to the control section 5.

The control section 5 has an MPU 51, a ROM 52, a RAM 53, a calculatingsection 54, a counter 55, a received data memory 56, a display section57, an operating section 58, etc. The MPU 51 controls other hardwaredevices in the oscillation section 3, receiving section 4 and controlsection 5, and executes various software functions, according tocomputer programs stored in the ROM 52.

The ROM 52 stores in advance various software programs necessary foroperating the touch panel device (control section 5). The RAM 53 storestemporary data produced during the execution of software. Thecalculating section 54 performs various calculation processes, includingthe process of calculating the contact position and contact width of anobject. The counter 55 sets the wave number of a burst wave. The wavenumber set in the counter 55 can be varied according to receivedstrength.

The received data memory 56 stores a time domain waveform obtained whenno object is in contact with the panel, a waveform obtained bysubtracting a predetermined slice value (threshold value) from the timedomain waveform, the slice value (threshold value), etc. The time domainwaveform obtained when no object is in contact with the panel isperiodically updated. Besides, the slice value (threshold value) is alsovariable. The display section 57 displays the operation state of thetouch panel device, and the contact position and contact width of theobject detected. The operating section 58 receives an operational inputentered by a user.

FIG. 4 is an illustration showing the configuration of the touch panelmain body 1. In FIG. 4, the numeral 11 represents a rectangularnon-piezoelectric substrate made, for example, of a glass material andcapable of propagating surface acoustic waves, and a center portionenclosed by the alternate long and short dashed line is a detectionregion 11 a capable of detecting the contact position. In a frame region11 b outside the detection region 11 a, which is a peripheral section ofthe non-piezoelectric substrate 11, excitation elements 12 forsimultaneously exciting surface acoustic waves in two directions areplaced on the upper side and the lower side of the frame region 11 b,and receiving elements 13 for simultaneously receiving surface acousticwaves from two directions are placed on the left side and the right sidethereof.

These excitation elements 12 and receiving elements 13 have the sameconfiguration, and each of the excitation elements 12 and receivingelements 13 is constructed by forming a comb-like electrode 15 on onesurface of a piezoelectric body 14 in the form of a thin film made ofAlN or ZnO, for example, and forming a plate electrode (solid electrode)16 on the other surface thereof. As shown in FIG. 4, the comb-likeelectrode 15 on the front side comprises a line of bus electrode 17 anda plurality of electrode fingers 18 which are extended from the buselectrode 17 and bent into V shape in the middle. The comb-likeelectrode 15 and the plate electrode 16 of each excitation element 12are connected to the oscillation section 3 of the touch panel drivedevice 2, and the comb-like electrode 15 and plate electrode 16 of eachreceiving element 13 are connected to the receiving section 4 of thetouch panel drive device 2. Note that, in FIG. 4, the plate electrodes16 are indicated by the broken lines, and the installation range of thepiezoelectric body 14 is indicated by the alternate long and shortdashed line.

In such a configuration, by applying a periodical signal between thecomb-like electrode 15 and the plate electrode 16, surface acousticwaves are simultaneously excited in two directions by the excitationelements 12, and the excited surface acoustic waves are propagated intwo diagonal directions of the non-piezoelectric substrate 11 andreceived by the receiving elements 13. More specifically, the surfaceacoustic waves from the upper-side excitation element 12 are propagatedin a lower left oblique direction and a lower right oblique directionand then received by the left-side and right-side receiving elements 13,while the surface acoustic waves from the lower-side excitation element12 are propagated in an upper left oblique direction and an upper rightoblique direction and then received by the left-side and right-sidereceiving elements 13. Here, when an object such as a finger or a pen isin contact with the propagation path of a surface acoustic wave on thenon-piezoelectric substrate 11, the surface acoustic wave attenuates.Therefore, by detecting the presence or absence of attenuation in thelevel of the received signals by the two receiving elements 13, it ispossible to detect the presence or absence of contact of the object andthe contact position.

In the present invention, according to the strength of the obtained timedomain waveform, the wave number of the burst wave applied to theexcitation element 12 is controlled so as to obtain a maximum gain ofthe time domain waveform. Besides, when detecting the contact positionof the object, an updatable threshold value is used instead of alwaysusing a determined fixed threshold value.

Next, the operation of the touch panel device having such aconfiguration will be explained. FIG. 5 is a flowchart showing theoperating procedure.

First, a frequency f₀ of the surface acoustic wave is set (step S1).More specifically, the set frequency f₀ is sent to the frequency counter33, and a parameter for oscillating the oscillator 32 at the frequencyf₀ is transmitted to the frequency controller 31. Next, an initial valuen of the wave number of the burst wave is set in the counter 55 (stepS2).

By using a pulse signal from the control section 5 as a trigger, theoscillation section 3 applies the burst wave only n times at thefrequency f₀ (step S3). As a result, the surface acoustic waves excitedby the excitation elements 12 propagate on the non-piezoelectricsubstrate 11 in diagonal directions and are received by the receivingelements 13, and the received signal waveform becomes a time domainwaveform (step S4). The strength of the obtained time domain waveform isfound, and it is judged whether or not the found strength is larger thana predetermined value (step S5).

If the found strength is smaller than the predetermined value (S5: NO),i.e., if sufficient received strength is not obtained, the wave numberof the burst wave in the counter 55 is incremented only by 1 (step S6),and the operation of S3 to S5 is repeated. The relationship between theincrease in the wave number of the burst wave and the received strengthwill be described in detail later.

If the found strength becomes larger than the predetermined value (S5:YES), i.e., if sufficient received strength is obtained, the wave numberof the burst wave at this time is stored (step S7), the time domainwaveform obtained at this time is smoothed (step S8), and then thesmoothed time domain waveform and a time domain waveform obtained bysubtracting a predetermined slice value (threshold value) from thesmoothed time domain waveform are stored temporarily as the time domainwaveforms of the comparison base in the received data memory 56 (stepS9). The smoothed time domain waveform will be hereinafter referred toas the reference time domain waveform, and the time domain waveformobtained by subtracting the slice value from the reference time domainwaveform will be hereinafter referred to as the slice time domainwaveform. This slice time domain waveform is a time domain waveform tobe compared when detecting the contact of an object. The smoothingprocess in S8 and the relationship among the reference time domainwaveform, the slice time domain waveform and the slice value (thresholdvalue) will be described in detail later.

After completing the above-described preparation steps, the calculationprocess for the contact position and contact width of the object isexecuted. In the condition in which the object is in contact with thetouch panel device, the oscillation section 3 applies the burst waveonly n times, which is stored in the counter 55, at the frequency f₀ toexcite the excitation elements 12, the excited surface acoustic wavesare propagated in the diagonal directions of the non-piezoelectricsubstrate 11 and received by the receiving elements 13, and the timedomain waveform is obtained (step S10). The same smoothing process as inS8 is performed on the obtained time domain waveform (step S11). Thetime domain waveform as a comparison object obtained when the object isin contact with the touch panel device will be hereinafter referred toas the actual time domain waveform.

The obtained actual time domain waveform is compared with the slice timedomain waveform stored in the received data memory 56 (step S12). Then,based on the comparison result, the contact position and the contactwidth of the object are calculated (step S13). The process of comparingthese two time domain waveforms and the calculation process for thecontact position and contact width of the object will be described indetail later. Next, it is judged whether or not an operational input tocomplete the detection process has been received (step S14), and, if ithas been received (S14: YES), the entire operations are completed.

If the detection process continues to be performed (S14: NO), it isjudged whether or not the time domain waveforms as the comparison base(reference time domain waveform and slice time domain waveform) are tobe updated (step S15). If they are not to be updated (S15: NO), theoperation of S10 to S14 is repeated to perform the next detection. Ifthe time domain waveforms as the comparison base are to be updated (S15:YES), the updating process is executed (step S16), and then theoperation of S10 to S14 is repeated. Thus, even in the actual detectionprocess, it is possible to update the time domain waveforms as thecomparison base. Since this updating process requires only 0.1 second orso, the updating process can be performed easily by choosing a timing inwhich the object is not in contact with the panel. A concrete techniqueof the updating process will be described in detail later.

The following description will explain the relationship between anincrease in the wave number of the burst wave and the received strengthin S2 to S6 of the flowchart in FIG. 5.

FIG. 6 is an illustration showing one example of the time domainwaveform. Since the surface acoustic wave propagating on thenon-piezoelectric substrate 11 attenuates according to the propagationdistance as shown in FIG. 6, the received strength is high at neardistances where the propagation distance is short (at early times), andthe received strength decreases gradually with an increase in thepropagation distance. In other words, when the surface acoustic wave isreceived at an early time, the strength of the surface acoustic wave ishigh, and the strength decreases at later reception time.

FIG. 7 is an illustration showing the difference in the time domainwaveform when the wave number of the burst wave is varied. In FIG. 7,the broken line indicates a time domain waveform when the wave number ofthe burst wave is set to n, and the solid line indicates a time domainwaveform when the wave number of the burst wave is set to (n+k).Further, the portion shown by hatching in FIG. 7 indicates a range inwhich the time domain waveform can be captured by the A/D converter 42of the receiving section 4.

The strength at time t₁ of the time domain waveform obtained by applyingthe burst wave n times is found, and it is judged whether or not thefound strength is sufficient (S5 in FIG. 5). For example, in the casewhere the result obtained by the A/D conversion at 10 MHz and 8 bits iscaptured in the memory in the control section 5 from an address 0 andthe strength is judged based on the received strength after t₁=10 μsfrom the start of receiving, the strength is judged based on thereceived strength at 10 μs×10 KHz=100, i.e., at the 100th byte from thetop.

In the case where the strength of the time domain waveform is A/Dconverted at 8 bits in the range of 0 to 255, when the strength iscloser to 255, the change in the time domain waveform can be representedby a larger number of bits, thereby enabling more accurate detection ofcontact of the object. Moreover, as the received strength increases, theshape of the time domain waveform is stabilized by an improvement ofS/N, thereby reducing erroneous detection of contact. For example, ifstrength G₁ when the wave number of the burst wave is n is 100, onlyabout 39% of receivable strength 255 is received.

Therefore, the wave number of the burst wave is increased by setting nn+1 (S6 in FIG. 5), and the same process is performed. When an idealreceived strength of the time domain waveform is set at 95% ofreceivable received strength, the same process (S3 to S6 in FIG. 5) isrepeated until received strength G₂ at the wave number (n+k) of theburst wave exceeds 242. Then, the wave number (n+k) of this case isstored in the counter 55 (S7 in FIG. 5).

Next, the smoothing process of S8 of the flowchart in FIG. 5 will beexplained. FIG. 8 is an illustration showing the time domain waveformincluding noise N. In the smoothing process, such noise N is eliminatedby a moving-average method, for example. For instance, in the case wherea moving average of 5 points is used, when sampling data (digital data)of the time domain waveform are captured in the order V_(k−2), V_(k−1),V_(k), V_(k+1), and V_(k+2) and the kth data is to be obtained, the dataitself and the preceding and succeeding data are multiplied by acoefficient as a weight. More specifically, data V_(k)′ after smoothedis calculated as shown by (1) below.V _(k)′=(−3V _(k−2)+12V _(k−1)+17V _(k)+12V _(k+1)−3V _(k+2))/35  (1)

The reference time domain waveform obtained by eliminating noise by sucha smoothing process is stored in the received data memory 56 (S9 in FIG.5). Moreover, the slice time domain waveform obtained by subtracting apredetermined slice value from the reference time domain waveform isalso stored in the received data memory 56 (S9 in FIG. 5). FIG. 9 is anillustration showing such time domain waveforms as the comparison base.In FIG. 9, the solid line represents the reference time domain waveform,and the broken line represents the slice time domain waveform obtainedby subtracting the slice value from the reference time domain waveform.

Next, the following description will explain the calculation process forthe contact position and contact width of the object, in S10 to S13 ofthe flowchart in FIG. 5.

(First Calculation Process)

The following explains the first technique for calculating the contactposition and contact width of the object from the attenuation startposition and attenuation end position of surface acoustic waves and thewave number of the burst wave. FIG. 10 is an illustration showing theprinciple of obtaining the attenuation start position and theattenuation end position, and FIG. 11 is an illustration showing theprinciple of calculating the contact position and the contact width.

In FIG. 10, the solid line represents the actual time domain waveformobtained in S10 and S11 in FIG. 5, and the broken line represents thestored slice time domain waveform. These two time domain waveforms arecompared (S12 in FIG. 5), and the relationship in which the strength ofthe actual time domain waveform<the strength of the slice time domainwaveform is seen when the surface acoustic waves attenuate because ofthe contact of the object. Thus, a time point at which this relationshipfirst appears is the attenuation start point, and the data address t₁ ofthis point is obtained. Thereafter, a time point at which theirrelationship in the magnitude of strength is reversed is the attenuationend point, and the data address t₂ of this point is obtained.

As shown in FIG. 11, an x-y coordinate system with its origin at thecenter of the square panel and the orthogonal x axis and y axis lying indiagonal directions is set, and a half the length of a diagonal line ofthe panel is denoted by L. Besides, suppose that attenuation (the voidportion in FIG. 11) is seen in the range where y>0. When the propagationvelocity of surface acoustic waves on the panel is denoted by v, theattenuation start position (contact start position) y_(i) and theattenuation end position (contact end position) y₂ are respectivelycalculated using t₁ and t₂ as shown by equations (2) and (3) below.y _(i) =L−vt ₁/2  (2)y ₂ =L−vt ₂/2  (3)Further, the contact width w and the center of gravity g of the contactarea are respectively calculated as shown by equations (4) and (5)below.w=v(t ₂ −t ₁)/2  (4)g=L−v(t ₁ −t ₂)/4  (5)(Second Calculation Process)

The following explains the second technique for calculating the contactposition and contact width of the object from the attenuation startposition and maximum attenuation position of surface acoustic waves andthe wave number of the burst wave. FIG. 12 is an illustration showingthe principle of obtaining the attenuation start position and themaximum attenuation position, and FIG. 13 is an illustration showing theprinciple of calculating the contact position and the contact width.

In FIG. 12, the solid line represents the actual time domain waveformobtained in S10 and S11 in FIG. 5, and the broken line represents thestored slice time domain waveform. The two time domain waveforms arecompared (S12 in FIG. 5), and a time point at which the relationship inwhich the strength of the actual time domain waveform<the strength ofthe slice time domain waveform first appears is determined to be theattenuation start point and the data address t₁ of this point isobtained in the same manner as in the first calculation process. Next,after the attenuation start point is determined, the attenuation that isthe difference between the two time domain waveforms is successivelycalculated and stored in the RAM 53 in the control section 5. Then, atime point at which the difference (attenuation) is a maximum isdetermined to be the maximum attenuation point, and the data address t₃of this point is obtained.

In FIG. 13, in the x-y coordinate system set in the same manner as inFIG. 11, suppose that attenuation (the void portion in FIG. 13) is seenin the range where y>0. The attenuation start position (the contactstart position) y_(i) and the maximum attenuation position (the centerof gravity of contact position) y₃ are respectively calculated using t₁and t₃ as shown by equations (6) and (7) below.y _(i) =L−vt ₁/2  (6)y ₂ =L−vt ₃/2  (7)Further, the contact width w is calculated as shown by equation (8)below.w=v(t ₃ −t ₁)  (8)

Note that the above first and second calculation processes are explainedfor the case where there is attenuation in the range of y>0. However,even in the case where there is attenuation in the respective ranges ofy<0, x>0, or x<0, it is of course possible to similarly calculate theattenuation start position, the attenuation end position, the maximumattenuation position, and the contact width. Further, based on thesecalculated values in the x direction and the y direction, the contactposition and the contact width of the object are detected.

Next, the following explains an update process for the time domainwaveforms as the comparison base in S15 of the flowchart in FIG. 5.Attenuation similar to that seen when the object is in touch with thepanel is sometimes seen constantly, including the time in which theobject is not in contact with the panel, because of adhesion of dirtsuch as finger prints to the panel. FIG. 14 is an illustration showingthe time domain waveforms when such dirt is adhering to the panel.

In FIG. 14, the solid line represents the actual time domain waveformobtained when dirt is adhering to the panel, and the broken linerepresents the slice time domain waveform obtained when no dirt isadhering to the panel. As shown in FIG. 14, even when no object is incontact with the panel, the received strength attenuates because of thedirt adhering to the panel. Hence, in such a case, when the time domainwaveform (solid line) is compared with the slice time domain waveform(broken line), erroneous detection is made due to the dirt. In order toavoid such a circumstance, in the present invention, the time domainwaveforms as the comparison base are updated newly based on the actualtime domain waveform (solid line) influenced by the dirt (S15 in FIG.5).

Such an update process is carried out by, for example, a techniquedescribed below. When the values of the reference time domain waveformas the comparison base are A[1], A[2], . . . , A[N] (N is the number ofsamplings) and the values of the actual time domain waveform are B[1],B[2], . . . , B[N], the value C[1] (1≦i≦N) of the reference time domainwaveform after update is given by C[1]=(A[1]+B[1])/2,C[2]=(A[2]+B[2])/2, C[N]=(A[N]+B[N])/2. By subtracting a predeterminedslice value from the new reference time domain waveform thus obtained,the slice time domain waveform after update is obtained.

These reference time domain waveform and slice time domain waveformafter update are stored in the received data memory 56. FIG. 15 is anillustration showing the reference time domain waveform and slice timedomain waveform after update, and the solid line represents thereference time domain waveform after update and the broken linerepresents the slice time domain waveform after update. By using theslice time domain waveform as shown in FIG. 15 in the comparisonprocess, it is possible to avoid erroneous detection when the panel isdirty.

Next, the following explains the process to be performed when aplurality of contact positions are detected. FIG. 16 is an illustrationshowing the relationship between the actual time domain waveform (solidline) and the slice time domain waveform (broken line) when contactpositions are detected at two points. In such a case, the contact widthsat the respective contact positions a and b are calculated, and thecontact position with a larger contact width is validated, while thecontact position with a smaller contact width is invalidated so as todetect a correct contact position.

FIG. 17 is a flowchart showing the operating procedure for determiningone correct contact position from a plurality of contact positions,based on the contact width. In the following explanation, i is the countof the counter that shows the position of a sampling point, B[i] is theith value of the actual time domain waveform, D[i] is the ith value ofthe slice time domain waveform, P is the calculated contact position, Wis the calculated contact width, p is a variable of the contact positionto be temporarily stored, and w is a variable of the contact width to betemporarily stored.

First, initialization (i=1, p=0, w=0) is performed (step S21). D[i] ofthe slice time domain waveform and B[i] of the actual time domainwaveform are read (steps S22 and S23), and it is judged whetherB[i]<D[i] (step S24). If B[i]<D[i] is not satisfied (S24: NO), since noobject is in contact with the panel, the current read position i isconfirmed and, if reading has not been performed to the end (step S33:NO), the count i of the counter is incremented by only 1 (step S34) andthe operations is repeated from S22.

If B[i]<D[i] is satisfied (S24: YES), since an object is in contact withthe panel, the current read position i is stored as the contact positionP (step S25). Next, after incrementing the count i of the counter byonly 1 (step S26), D[i] of the slice time domain waveform and B[i] ofthe actual time domain waveform are read (steps S27 and S28), and it isjudged whether B[i]>D[i] (step S29). If B[i]>D[i] is not satisfied (S29:NO), since the object continues to be in contact with the panel, theoperations is repeated from S26.

On the other hand, if B[i]>D[i] is satisfied (S29: YES), since theobject is no longer in contact with the panel, the contact width W atthis time is calculated (step S30). It is judged whether or not thecalculated W is larger than w (step S31), and if W is larger than w(S31: YES), the calculated W is set as w and the contact position P atthis time is set as p (step S32). If W is smaller than w (S31: NO), thevalues of w and p are not changed.

Then, the current read position i is confirmed, and it is judged whetheror not reading has been performed to the end (S33). If reading has notbeen performed to the end (S33: NO), the count i of the counter isincremented by only 1 (S34), and the operation is repeated from S22. Ifreading has been performed to the end (S33: YES), the values set for pand w (contact position and contact width) are outputted (step S35).

Next, the following explains the process of correcting the receivedstrength, according to the propagation distance of surface acousticwaves. As described above, as the propagation distance increases, thedegree of attenuation increases, and therefore the time domain waveformattenuates (see FIG. 6). Hence, in the present invention, by taking intoaccount the attenuation due to propagation, a decrease in the receivedstrength is corrected, and consequently the time domain waveform issmoothed.

FIG. 18 is an illustration explaining the principle of such a correctionprocess (smoothing process). In FIG. 18, a solid line S represents thetime domain waveform before corrected (before smoothed), and a solidline T represents the time domain waveform after corrected (aftersmoothed).

Since the time domain waveform is converted into digital data by the A/Dconverter 42, the correction is performed by multiplying the respectivedigital data by a coefficient. When the panel size is 3 inches, themaximum value from the amplifier 41 is about twice larger than theminimum value. Specifically, when the time domain waveform is A/Dconverted at 8-bit, 256 resolution, if the maximum value is 200, theminimum value is 100. Here, if the sampling points are 100 points,received strength V(i) at the ith point is corrected as shown byequation (9) below. When the strength at the 100th point becomes a halfof the strength at the 1st point due to attenuation, if the strength atthe 1st point is denoted by A and the strength at the 100th point iscalculated according to expression (9) below, then A is given as shownby equation (10) below, thereby correcting the attenuation caused bypropagation.V(i)/(1−0.005i)  (9)0.5A/(1−0.005×100)=A  (10)

Next, the following explains the process of selecting an abnormalcontact position among a plurality of finally detected contact positionsand eliminating it. FIG. 19 is an illustration showing the principle ofthis process. The contact position is detected every fixed timeinterval. In addition, since the moving speed of the object in contactwith the panel is limited, if the movement of the contact position islarger than a predetermined value, the detected contact position(contact position 3 in FIG. 19) is regarded as noise and invalidated.

For example, if the number of times of detecting the contact position is200 times per second and the maximum moving speed of the object is 100cm per second, then the maximum movement of the contact position is 0.5cm. Therefore, when the movement is more than 0.5 cm (for example, whenthe distance between the contact positions 2 and 3 in FIG. 19 is 1 cm),the contact position 3 is regarded as noise and eliminated. Further, acurve passing through the contact positions 1, 2, 4, 5, 6 and 7 isregarded as the path of the object.

Note that although the above-described embodiment illustrates a touchpanel device having the structure in which surface acoustic waves arepropagated in the diagonal directions of the square panel (see FIG. 4),it is of course possible to similarly apply the present invention to atouch panel device having the structure in which surface acoustic wavesare propagated in the side directions of the square panel (see FIG. 2).

As described in detail above, in the present invention, since the wavenumber of the burst wave to be applied to exciting means is controlledbased on the strength of the received surface acoustic waves, even whenthe strength of the time domain waveform changes because of fingerprints, etc., a stable touch sensitivity can always be obtained.Moreover, even when the touch panel is dirty, the contact position ofthe object can be highly accurately detected without applying highpressure of the object (tool force).

Furthermore, in the present invention, since the obtained time domainwaveform is smoothed, it is possible to eliminate the influence ofnoise, and improve the detection accuracy of the contact position.

Besides, in the present invention, since a contact position is detectedbased on the received results of surface acoustic waves which arereceived when no object is in contact with the panel and the receivedresults of surface acoustic waves which are received when an object isin contact with the panel, even when the panel is dirty and the touchsensitivity is low, it is possible to correctly detect the contactposition of the object without using a fixed threshold value which isdetermined during design or activation in a conventional art.

Additionally, in the present invention, since the received results ofsurface acoustic waves which are received when no object is in contactwith the panel and are stored are periodically updated, it is possibleto detect the contact position without being influenced by constantchange in the time domain waveform caused by dirt on the panel.

Moreover, in the present invention, since the contact position and/orthe contact width of the object are detected based on the attenuationstart position and attenuation end position and the wave number of theburst wave, or based on the attenuation start position and maximumattenuation position and the wave number of the burst wave, it ispossible to correct the deviation of the contact position due to thewave number of the burst wave, and improve the detection accuracy.

Furthermore, in the present invention, when a plurality of contactpositions are detected, since the contact position with the largestcontact width is selected, it is possible to identify the correctcontact position.

Besides, in the present invention, since the strength of the time domainwaveform is corrected according to the propagation distance, it ispossible to achieve uniform detection sensitivity on the panel.

Further, in the present invention, when the distance between the contactpositions detected every fixed time interval is longer than apredetermined value, since the contact position is invalidated, it ispossible to eliminate an erroneously detected contact position.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within metesand bounds of the claims, or equivalence of such metes and boundsthereof are therefore intended to be embraced by the claims.

1. A touch panel device having at least one pair of excitation sectionfor exciting surface acoustic waves by application of a burst wave andreceiving section for receiving surface acoustic waves at a storingperiod and a detecting period, which are arranged to face each other ona substrate capable of propagating surface acoustic waves, forpropagating surface acoustic waves between said excitation section andsaid receiving section on said substrate and detecting presence orabsence of an object in contact with said substrate, based on receivedresults by said receiving section, said touch panel device comprising: astoring section for storing a surface acoustic wave received at saidstoring period by said receiving section as a comparison base surfaceacoustic wave; an obtaining section for obtaining a surface acousticwave received at said detecting period by said receiving section as acomparison object surface acoustic wave; and a comparing section forperforming a comparison of said comparison base surface acoustic waveand said comparison object surface acoustic wave, wherein said storingperiod and said detecting period are periodically repeated,respectively, when a result of the comparison indicates that saidcomparison object surface acoustic wave has been changed from saidcomparison base surface acoustic wave, said touch panel device detectsthat said of objects has been present, and said surface acoustic wavereceived at said storing period by said receiving section is notutilized as said comparison object surface acoustic wave.
 2. The touchpanel device of claim 1, further comprising an updating section forupdating the received results stored in said storing section.
 3. Thetouch panel device of claim 2, further comprising: a calculating sectionfor calculating an attenuation start position and an attenuation endposition of received surface acoustic waves, based on a comparisonresult obtained by said comparing section; and a detecting section fordetecting a contact position and/or a contact width of the object, basedon the attenuation start position and attenuation end positioncalculated by said calculating section and the wave number of the burstwave applied to said excitation section.
 4. The touch panel device ofclaim 2, further comprising: a calculating section for calculating anattenuation start position and a maximum attenuation position ofreceived surface acoustic waves, based on a comparison result obtainedby said comparing section; and a detecting section for detecting acontact position and/or a contact width of the object, based on theattenuation start position and maximum attenuation position calculatedby said calculating section and the wave number of the burst waveapplied to said excitation section.
 5. The touch panel device of claim1, further comprising: a calculating section for calculating anattenuation start position and an attenuation end position of receivedsurface acoustic waves, based on a comparison result obtained by saidcomparing section; and a detecting section for detecting a contactposition and/or a contact width of the object, based on the attenuationstart position and attenuation end position calculated by saidcalculating section and the wave number of the burst wave applied tosaid excitation section.
 6. The touch panel device of claim 1, furthercomprising: a calculating section for calculating an attenuation startposition and a maximum attenuation position of received surface acousticwaves, based on a comparison result obtained by said comparing section;and a detecting section for detecting a contact position and/or acontact width of the object, based on the attenuation start position andmaximum attenuation position calculated by said calculating section andthe wave number of the burst wave applied to said excitation section. 7.The touch panel device of claim 1 further comprising a correctingsection for correcting strength of surface acoustic waves received bysaid receiving section, according to propagation distances of thesurface acoustic waves.